System and method for gatekeeper-to-gatekeeper communication

ABSTRACT

A method for communication employs a plurality of gatekeepers and involves receiving at a first gatekeeper a request for information. If the information is not known by the first gatekeeper, a request is sent via a second gatekeeper to a third gatekeeper for the information. If the information is known by the third gatekeeper, it is returned to the first gatekeeper, illustratively via the second gatekeeper. The gatekeepers are at a single gatekeeper hierarchical level.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 09/328,667filed Jun. 9, 1999, now U.S. Pat. No. 6,965,591 which claimed thebenefit of U.S. Provisional Application No. 60/100,130, filed Sep. 14,1998.

FIELD OF THE INVENTION

The present invention involves network communication. In particular, thepresent invention introduces systems and methods forgatekeeper-to-gatekeeper communication for any combination of inter-zoneand inter-domain gatekeepers.

BACKGROUND

The International Telecommunication Union-Telecommunication (ITU-T) hasdeveloped a recommended standard for Packet-Based MultimediaCommunications Systems. The standard is called H.323. The recommendationenvisions that there can be one or more zones in a given H.323communications system. A zone can contain H.323 functional entities suchas terminals, gateways, multipoint control units (MCUs), communicationsnetworks, and their resources including bandwidth, ports, buffers, andothers.

H.323 mandates that a functional entity, which is called a gatekeeper,manages the resources within a given zone. A gatekeeper is anintelligent functional entity used to transfer signaling messages intoand out of zones and domains, and contains the intelligence necessary toestablish communication between communicating entities. Typically, thegatekeeper manages a single zone.

H.323 systems, however, are not limited to single zones. In fact, alarge H.323 system can consist of multiple zones with a boundary betweenthe zones. The zone boundary can be physical or logical.

While the H.323 standard defines certain requirements, the standard doeshave some gaps. For example, typically, certain H.323 signaling messagesare transmitted between H.323 entities and the gatekeeper in a givenzone only. These signaling messages include location, zone admission,bandwidth, discovery, registration, and/or other signaling messages.These messages, however, may have to travel between multiple gatekeepersin their respective source-destination paths because the first receivinggatekeeper may not be able to process the signaling message. If thefirst gatekeeper cannot process the signaling message, it is sent forprocessing to another zone's gatekeeper. The H.323 standards do notspecify how these signaling messages can be sent between the gatekeepersin a multiple-gatekeeper environment.

Further gaps exist in H.323 requirements. For example, H.323 does notspecify the possible logical architectural relationships between thegatekeepers for communications. If the gatekeepers are arranged in ahierarchical relationship, a hierarchical gatekeeper architecture maynot even maintain a zone. Rather, the gatekeeper may manage a number ofgatekeepers that maintain the respective zones. In a distributednon-hierarchical gatekeeper architecture, there are no specifiedmechanisms for signaling between gatekeepers.

In addition, H.323 does not provide any caching management mechanismsfor the information to be acquired dynamically between the gatekeepers.Moreover, there is no notion of gatekeeper-level routing so thatmessages can be sent between the gatekeeper for resolving the requiredinformation where multiple gatekeepers are involved. These signalingmessages lack the required fields that will facilitate the notion ofrouting between the gatekeepers considering the multiple gatekeeperseither in multiple zones of the giving domain and/or in multiple domainswhere a domain consists of one or more zones.

SUMMARY OF THE INVENTION

To alleviate the problems in the prior art, the present inventionintroduces systems and methods for communication usinggatekeeper-to-gatekeeper communication, using both inter-zone andinter-domain protocols and architectures. The invention facilitatesinter-gatekeeper communications among the zones either in a givendomain, or between domains, in a distributed, hierarchical, or hybrid(distributed and hierarchical) architecture. This can be done in severalways. For example, but not the only example, intergatekeepercommunication can be facilitated by dynamically acquiring knowledge ofthe destinations served by other gatekeepers, or resources,quality-of-service, security features, pricing, traffic, and otherinformation. As another example, but not the only example,intergatekeeper communication can be facilitated by various types ofcache management and extension of the existing H.323 signaling messages.

In one embodiment of the present invention, a method for communicationis disclosed, the method comprising the steps of receiving at a firstgatekeeper a request for information and determining whether theinformation is known by the first gatekeeper. If the information is notknown by the first gatekeeper, the request is sent via a logicalgatekeeper-level path to a second gatekeeper. If the second gatekeeperknows the information, it sends the information, via a logicalgatekeeper-level path, to the first gatekeeper.

It should be noted that a gatekeeper is an application-level entity. Thelower network (e.g., routers) or link (e.g., switches) layer entitiesperform actual routing of messages among themselves to send thesignaling messages between the gatekeepers at the instantiation of theapplication-layer gatekeeper request.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system overview of an embodiment of the present inventionfor inter-zone communications in which one gatekeeper in a given zone iscommunicating with other gatekeepers in adistributive-gatekeeper-architecture requirement.

FIG. 2 is a system overview of an embodiment of the present inventionfor inter-domain communications in ahierarchical-gatekeeper-architecture environment.

FIG. 3 is a system overview of an embodiment of the present inventionfor inter-domain communications in a layeredhierarchical-gatekeeper-architecture environment.

FIG. 4 is a system overview of an embodiment of the present inventionfor inter-domain communications in a hybrid gatekeeper-architectureenvironment.

FIG. 5 is a flow chart depicting an embodiment of the present invention.

FIG. 6 is a block diagram of an embodiment of the present inventioncomprising a processor and a memory.

DETAILED DESCRIPTION

The present invention provides systems and methods for efficientinter-zone or inter-network communication using agatekeeper-to-gatekeeper protocol.

FIG. 1 is a system overview of a distributed gatekeeper system in whicheach gatekeeper manages and controls to its zone. Note that eachgatekeeper does not have to be tied to a specific zone based on aphysical boundary. The zone boundary can be logical, as well.Additionally, each gatekeeper can manage and control entry into adistinct domain or network, or there can be a combination of gatekeeperscontrolling any combination of zones and networks. Thus, for thepurposes of the present invention, the gatekeepers are not necessarilyinter-zoned gatekeepers. The gatekeepers can be inter-networkedgatekeepers such that each gatekeeper is connected to a differentnetwork or domain.

In FIG. 1, subscriber terminal 101 and other entities of zone 103 a cancommunicate with gatekeeper 102 a for sending, receiving and resolvinginformation. Similarly, subscriber terminal 105 (106) and other entitiesof zone 103 b (103 c) can communicate with gatekeeper 102 b (102 c).Gatekeeper 102 a can also interact with gatekeeper 102 b. Thus,gatekeeper 102 a can receive a request for information from subscriber101. Gatekeeper 102 a can pass the query along to gatekeeper 102 b.Gatekeeper 102 a can also contain a database in which gatekeeper 102 astores the requested information. Gatekeeper 102 b and 102 c in thisembodiment can receive and send queries, and can contain a database inwhich various information can be stored. This information includes, butis not limited to, addresses, pricing, quality of service, resources,security features, and other information. Note that FIG. 1 portraysgatekeepers 102 a through 102 c, although in general there can be anarbitrary number of gatekeepers.

In one embodiment of the present invention, gatekeeper 102 a can receivefrom subscriber 101 a query for some kind of information. Thisinformation can be any network address, the address of anapplication-layer resource, middleware-layer resource, transport-layerresource, and/or a network-layer resource. These resources can include,but are not limited to, bandwidth, ports, buffers, links/trunks, controlprocessing units (CPUs) capacity, and quality-of-service parameters.

After receiving the query, gatekeeper 102 a can attempt to resolve thequery by searching its database for the network address. If gatekeeper102 a cannot resolve the query, for example, if gatekeeper 102 a doesnot contain a requested IP address in its database, then gatekeeper 102a can query the next gatekeeper, in this case gatekeeper 102 b.Gatekeeper 102 b receives the query from gatekeeper 102 a, and againattempts to resolve the query by searching its database. If gatekeeper102 b cannot resolve the query, then gatekeeper 102 b passes the queryalong to the next gatekeeper, in this case gatekeeper 102 c. Thisprocess continues until a gatekeeper can resolve the query.

When gatekeeper 102 c resolves the query, that is, when gatekeeper 102 csearches its database and finds the requested network address, forexample, gatekeeper 102 c can send the network address back togatekeeper 102 a along the reverse path that the query was originallysent through gatekeeper 102 b. As each gatekeeper in the path receivesthe network address, it can store the information so that, in thefuture, the query can be resolved along a shorter path. Gatekeeper 102a, the originating gatekeeper, can pass the network address on tosubscriber 101 so that subscriber 101 can attempt to connect to theperson using the known network address. In another embodiment of thepresent invention, gatekeeper 102 a can route the call itself using thereceived network address.

Zones 103 a, 103 b and 103 c are bound by communication-system entity104. For the purposes of this application, a communication-system entitycan be a local area network, an Internet protocol network, anasynchronous transfer mode network, a frame relay network, and/or anyother network. Additionally, a communication-system entity like agatekeeper can be a middleware- or application-layer communicationentity embedded above the network layer. Routers or switches, however,are lower network-layer, or link-layer, entities. These lower-layerentities will actually route the message between themselves to send themessages at the instantiation of the application-layer entity like thegatekeeper. In this way, the messages can be send between gatekeepersvia the logical gatekeeper path.

Because the reply returns along the original path, all the intermediategatekeepers can cache the information for some predetermined amount oftime. The next time a subscriber requests that information, a gatekeepercan respond directly without forwarding the requests. Note that thereply does not have to traverse the original path, but can return alongsome variant of the original path. Additionally, the information doesnot necessarily have to be cached along the return path.

FIG. 2 is a system overview of a centralized gatekeeper system in whichgatekeepers are arranged in a hierarchical form. In this embodiment,gatekeeper 202 a is a centralized gatekeeper through which gatekeepers202 b, 202 c and 202 d interact. Gatekeepers 202 b, 202 c and 202 dmanage, in this Figure, zones 203 a, 203 b and 203 c, respectively. Asin the distributed architecture, these gatekeepers can manage domainsrather than zones. In this embodiment, gatekeeper 202 a does not manageany one zone or domain. Gatekeeper 202 a's function is to tie togetherthe various gatekeepers that are lower in the hierarchy (e.g., 202 b,202 c and 202 d). In another embodiment of the present invention, agatekeeper can be a centralized gatekeeper (connecting other gatekeeperstogether) while, at the same time, managing a zone or domain of its own.Note that the communication paths between the gatekeepers are alwayspredefined.

In the embodiment represented by FIG. 2, gatekeeper 202 b can receive arequest for information from terminal 201 a. Gatekeeper 202 b candetermine whether it has the requested information. If it does, it cansend the information to terminal 201 a.

If gatekeeper 202 b does not contain the requested information, it cansend a query to other gatekeepers through centralized gatekeeper 202 a.Gatekeeper 202 a can receive a request for information from gatekeeper202 b (or any gatekeeper) and can send that request to any gatekeeperbeneath it in the hierarchy. Alternatively, gatekeeper 202 a can knowwhich gatekeeper to contact for the information, and the request will besent to the corresponding gatekeeper by gatekeeper 202 a. Centralgatekeeper 202 a can keep all information of all gatekeepers in itsmemory (but this is not necessary), and sends the response to therequesting gatekeeper of the lower hierarchy.

FIG. 3 is an embodiment of the present invention in which thegatekeepers are arranged in a centralized or hierarchical form thatcontains multiple domains and multiple levels of hierarchicalgatekeepers. In this embodiment of the present invention, gatekeeper 301a is a centralized gatekeeper in the sense that it functions only toconnect other gatekeepers with one another, and does not manage anydomain or zone. In this embodiment, gatekeeper 301 a is logicallyconnected to gatekeepers 302 a, 302 b, and 302 c, all of which arecentralized or hierarchical gatekeepers in the same sense as gatekeeper301 a. Gatekeeper 302 a, for example, functions only to connectlogically gatekeepers 303 a and 303 b with each other; it does notmanage any domain or zone.

In another embodiment of the present invention, gatekeeper 301 a, 302 a,303 b and 303 c, or any combination thereof, can each manage a domain orzone while connecting other gatekeepers lower down in the hierarchy.

For example, gatekeeper 302 a manages domain 312 a, while domain 312 aconsists of two zones (not shown in FIG. 3) managed by gatekeepers 303 aand 303 b. This is, hierarchical gatekeeper 302 a has the knowledge ofthe domain to resolve information while the zonal gatekeepers canresolve information that is resident to their respective zones. The sameis true for domains 312 b and 312 n. Gatekeeper 301 a, however, has theknowledge to resolve information of all domains such as 312 a, 312 b,and 312 n. If gatekeepers 302 a, 302 b and 302 n are considered athierarchical level 1, gatekeeper 301 a can be considered at hierarchicallevel 2. Clearly, one can create many hierarchical levels ofgatekeepers. Conceptually, the communication between gatekeepers 301 a,302 a, 302 b and 302 n can be considered as inter-domain communications.For the sake of generality, one can consider that gatekeeper 301 amaintains its own domain.

FIG. 4 is a system overview of an embodiment of the present inventionfeaturing gatekeepers arranged in a hybrid architecture consisting ofboth distributed and centralized (or hierarchical) architecture. In thisembodiment, gatekeepers 420 a and 420 b communicate in a distributedenvironment with domain 423 a, each managing zones 422 a and 422 b,respectively. Centralized gatekeeper 420 c, in the meantime, managescommunication between gatekeepers 420 d, 420 e, and 420 f in domain 423b, while gatekeepers 420 d, 420 e and 420 f manage zones 422 c, 422 d,and 422 e, respectively.

In this Figure, communications between domains 423 a and 423 b occur viagatekeepers 420 b and 420 c.

The communication between gatekeepers within domain 423 a occurs in adistributed manner while gatekeepers in domain 423 b communicate in ahierarchical manner. The communication flow for requesting and receivinginformation in domain 423 a will take place as in a distributedgatekeeper architecture that has been described in the case of FIG. 1,while the communications in domain 423 b will take place in ahierarchical manner that has been described in the case of FIG. 2.Gatekeeper 420 b, however, will communicate with centralized gatekeeper420 c, and this form of communication will constitute inter-domaincommunication between domains 423 a and 423 b.

FIG. 5 is a flow chart of a method of practicing the present inventionaccording to at least one embodiment of the present invention. It shouldbe appreciated that the flow chart and the claims are not intended toimply a mandatory order to the invention. Rather, the steps of the flowchart and the steps of the claims can be performed in any practicableorder.

At step 501, a gatekeeper receives a request for information. Thisrequest for information can include a request to resolve a networkaddress, or a request for resource information such asapplication-layer, middleware-layer, transport-layer and/ornetwork-layer resources such as bandwidth, ports buffers, links/trunks,CPU capacity, and/or quality of service and performance parameters. Thequery can also contain registration, admission, and status signalingmessages. These signaling messages can be used by a gatekeeper to handlethe query.

At step 502, it is determined whether the requested information is knownby the first gatekeeper. If the information is known by the firstgatekeeper, then at step 503 the information is retrieved from thedatabase and the network address is returned to the querying entity inresponse to the query at step 504. If the information is not known bythe first gatekeeper, then at step 505 the query is passed to a secondgatekeeper. The choice of the second gatekeeper can be based on thedecision that will provide the best possible gatekeeper-level logicalpath through which the signaling message will be routed between thegatekeepers. At step 506, the information is received from the secondgatekeeper. The response to the query will always be received from thesecond gatekeeper (if the second gatekeeper is queried). This isbecause, even if the second gatekeeper cannot resolve the query, theresolved query will be returned to the first gatekeeper along a reversepath that the query originally travels.

At step 507, the received information is stored in the firstgatekeeper's database. At step 508, the address is returned by the firstgatekeeper in response to the originally-received query.

The gatekeeper serving the destination of the request for information(i.e., the last gatekeeper in the chain) can cache all resolutionrequests to which it has responded. The cache can help this gatekeeperto issue a “deregistration” or “parameter change” (e.g., bandwidthchange) request if the information from all resolution requests to whichit has responded in the reply has the possibility of changing during itslifetime.

In a multiple gatekeeper environment, a maximum limit can be providedfor how many gatekeepers that a request can traverse before beingdiscarded. This field can be defined as a hop count. The hop countindicates the maximum number of hop counts between the gatekeepers thata signaling message is allowed to traverse before being discarded. Thisfield is set based on a design parameter beyond the scope of thisinvention, and its value depends on the specific implementation schemeof the underlying transport networking technologies.

In one embodiment of the present invention, each gatekeeper decrementsthe hop count by a quantity depending on the value that is beingallocated for a path as the signaling message transits the gatekeeper onits way to the next gatekeeper along the logical-gatekeeper-routed pathto the destination. If a gatekeeper receives a message that should beforwarded to another gatekeeper, and that message contains a hop countset to zero, then the gatekeeper sends an error-indication message backto the source entity, and the message is dropped. If a respondinggatekeeper replies to the request, then a gatekeeper places a value inhop count as if it were sending a request of its own.

Using this hop count, each gatekeeper can decrement this hop-count fieldas a signaling message transits the gatekeeper on the way to the nextgatekeeper along the path to the destination. The gatekeeper-level hopcount is only considered in the context of the number of gatekeepers.Between any two gatekeepers, however, there can be one or many network(e.g. routers) or link (e.g., switches) layer entities that actuallyroute the packets or calls among themselves. This application-layer hopcount can be translated into the corresponding lower networking-layerhop count or other functional entities as appropriate depending on thecorresponding transport networking technologies. In other words, the hopcount is not limited to counting gatekeepers; the hop count can measurecounting other entities as well.

In another embodiment of the present invention, the response to thequery is assigned a time-to-live field. This field specifies the holdingtime for which the response to the query is considered valid. In thiscontext, if the response to the query is cached, the cached informationis valid up to the time specified in the time-to-live field. Thus, atransit gatekeeper lying along the path between the source entity andthe responding gatekeeper can cache source binding information containedin the resolution message that it can then forward if the time-to-livevalue is greater than zero.

There are a number of other fields that can be sent in the request forinformation from one gatekeeper to another. These fields include, butare not limited to, a field keeping track of the various gatekeeperidentifiers (i.e., a way of using data to refer to the variousgatekeepers) and a field relating to end of the query chain at which theinformation is known.

In one embodiment of the present invention, when an entity desiresinformation, it can use the corresponding registration, admission andstatus signaling message with an extension of the hop count, gatekeeperidentifier and the last entity in the query chain. These additionalthree fields facilitate routing signaling messages between gatekeepersusing the notion of the gatekeeper-level path to avoid looping and otherassociated problems.

If a determination is made that no gatekeeper in the system can reply tothe request for the destination address, then a negative reply isreturned.

FIG. 6 is a block diagram of an apparatus according to an embodiment ofthe present invention. In this embodiment, processor 601 is coupled tosaid port 602. Port 602 can receive a query and send a response to aquery. Memory 603 is coupled to said processor 601. Memory 603 storesthe instructions adapted to run on said processor to perform any methodembodiment of the present invention. For example, memory 603 can storeinstructions adapted to be run on processor 601 to receive a request forinformation, determine whether the information is known by thegatekeeper, and if not, passing the query to another gatekeeper. Inresponse the information can be received from the other gatekeeper,stored in memory 602 a, and returned to querying entity. Memory 603 cancontain database 603 a. Database 603 a can store network addresses thatcan be retrieve and passed along to processor 601 for transmissionthrough port 602.

For the purposes of this application, memory includes any medium capableof storing instructions adapted to be executed by a processor. Someexamples of such media include, but are not limited to, RAM, ROM, floppydisks, CDROM, magnetic tape, hard drives, optical storage units, and anyother device that can store digital information. In one embodiment, theinstructions are stored on the medium in a compressed and/or encryptedformat. As used herein, the phrase “adapted to be executed by aprocessor” is meant to encompass instructions stored in a compressedand/or encrypted format, as well as instructions that have to becompiled or installed by an installer before being executed by theprocessor.

The present invention has been described in terms of several embodimentssolely for the purpose of illustration. Persons skilled in the art willrecognize from this description that the invention is not limited to theembodiments described, but may be practiced with modifications andalterations limited only by the spirit and scope of the appended claims.

1. A method for use in a communication system, the communication systemincluding at least first, second and third gatekeepers having respectiveassociated subscriber terminals, the method comprising the firstgatekeeper receiving a request for information from one of itsassociated subscriber terminals; if the information is not known by thefirst gatekeeper, the first gatekeeper sending the request only to thesecond gatekeeper, if the information is not known by the secondgatekeeper, the second gatekeeper sending the request only to the thirdgatekeeper, and if the information is known by the third gatekeeper, thethird gatekeeper sending the information to the first gatekeeper,wherein each of the first, second and third gatekeepers communicateswith its respective associated subscriber terminals over a respectivecommunication path that does not include any other gatekeeper, whereineach of the first, second and third gatekeepers establishescommunication among its associated subscriber terminals, and wherein thecommunication between the subscriber terminals associated with the firstgatekeeper passes through no gatekeeper other than the first gatekeeper,the communication between the subscriber terminals associated with thesecond gatekeeper passes through no gatekeeper other than the secondgatekeeper, and the communication between the subscriber terminalsassociated with the third gatekeeper passes through no gatekeeper otherthan the third gatekeeper.
 2. The method of claim 1 wherein the thirdgatekeeper sends the information to the first gatekeeper via the secondgatekeeper.
 3. The method of claim 1 wherein the requested informationis an address.
 4. The method of claim 3 wherein said address is anapplication address, a network address or a resource address.
 5. Themethod of claim 1 wherein the requested information is information abouta resource.
 6. The method of claim 5 wherein said resource is one of:bandwidth, a port, a buffer, a link, a trunk, processing unit capacity,and a quality-of-service parameter.
 7. The method of claim 1 whereineach of the gatekeepers is adapted to use signaling messages conformingto International Telecommunications Union standard H.323 to receive andtransmit information between at least itself and its respectivesubscriber terminals.
 8. A communication system comprising at leastfirst, second and third gatekeepers and a plurality of communicatingentities, the first, second and third gatekeepers being configured toreceive and transmit signaling messages among themselves, wherein thefirst gatekeeper directly communicates gatekeeper-to-gatekeeperinformation request signaling messages only with the second gatekeeper,wherein the second gatekeeper directly communicatesgatekeeper-to-gatekeeper information request signaling messages with thefirst gatekeeper and the third gatekeeper, wherein the third gatekeeperdirectly communicates gatekeeper-to-gatekeeper information requestsignaling messages with the second gatekeeper but not with the firstgatekeeper, wherein the first, second and third gatekeepers are all at asingle gatekeeper hierarchical level within the communication system,wherein each of the first, second and third gatekeepers is configured toreceive and transmit signaling messages between itself and associatedones of the communicating entities over a respective communication paththat does not include any other gatekeeper, wherein each of the first,second and third gatekeepers is further configured to establishcommunication between its associated communicating entities, and whereinthe communication between the communicating entities associated with thefirst gatekeeper passes through no gatekeeper other than the firstgatekeeper, the communication between the communicating entitiesassociated with the second gatekeeper passes through no gatekeeper otherthan the second gatekeeper, and the communication between thecommunicating entities associated with the third gatekeeper passesthrough no gatekeeper other than the third gatekeeper.
 9. The system ofclaim 8 wherein ones of said gatekeeper-to-gatekeeper signaling messagesinclude requests for at least one of an application address, a networkaddress and a resource address.
 10. The system of claim 8 wherein onesof said gatekeeper-to-gatekeeper signaling messages include requests forinformation about a resource.
 11. The system of claim 10 wherein saidresource is one of: bandwidth, a port, a buffer, a link, a trunk,processing unit capacity, and a quality-of-service parameter.
 12. Thesystem of claim 8 wherein at least said gatekeeper-to-gatekeepersignaling messages conform to an international standard for packet-basedcommunications.
 13. The system of claim 8 wherein at least ones of thecommunicating entities are terminals, gateways, multipoint control unitsor communication networks.
 14. The system of claim 1 wherein the firstgatekeeper is configured to cache information received by the firstgatekeeper from another one of the gatekeepers so that if the firstgatekeeper is again requested for said information, the first gatekeeperwill be able to provide said information to the source of the request.15. The system of claim 8 wherein each particular gatekeeper thatreceives requested information from another one of the gatekeepersstores that information within that particular gatekeeper so that ifthat particular gatekeeper is again requested for said information, itwill be able to provide said information to the source of the request.16. A method for use in a communication system in which at least first,second and third gatekeepers are each connected to one or moreassociated subscriber terminals via one or more networks, in which eachof the at least first, second and third gatekeepers has a respectiveassociated database, and in which each of the at least first, second andthird gatekeepers, in response to a request for information from arequesting one of its associated subscriber terminals, provides therequested information from that gatekeeper's associated database to therequesting subscriber terminal if that gatekeeper's associated databasecontains the requested information, the method comprising the firstgatekeeper receiving from a requesting one of its associated subscriberterminals a request for information that is not contained in thedatabase associated with the first gatekeeper, the first gatekeepersending the request only to the second gatekeeper, if the information isnot contained in the database associated with the second gatekeeper, thesecond gatekeeper sending the request only to the third gatekeeper, andif the information is contained in the database associated with thethird gatekeeper, the third gatekeeper sending the information to thefirst gatekeeper, wherein each of the first, second and thirdgatekeepers is configured to receive and transmit signaling messagesbetween itself and its associated subscriber terminals over a respectivecommunication path that does not include any other gatekeeper, whereineach of the first, second and third gatekeepers is further configured toestablish communication between its associated subscriber terminals, andwherein the communication between the subscriber terminals associatedwith the first gatekeeper passes through no gatekeeper other than thefirst gatekeeper, the communication between the subscriber terminalsassociated with the second gatekeeper passes through no gatekeeper otherthan the second gatekeeper, and the communication between the subscriberterminals associated with the third gatekeeper passes through nogatekeeper other than the third gatekeeper.
 17. The invention of claim16 wherein the third gatekeeper sends the information to the firstgatekeeper via the second gatekeeper.
 18. The invention of claim 16wherein the requested information is an address.
 19. The invention ofclaim 18 wherein said address is an application address, a networkaddress or a resource address.
 20. The invention of claim 16 wherein therequested information is information about a resource.
 21. The inventionof claim 20 wherein said resource is one of: bandwidth, a port, abuffer, a link, a trunk, processing unit capacity, and aquality-of-service parameter.
 22. The invention of claim 16 wherein eachof the gatekeepers is configured to use signaling messages conforming toInternational Telecommunications Union standard H.323 to receive andtransmit information between at least itself and its respectivesubscriber terminals.